The present invention relates to a useful thermoplastic resin composition and more particularly to a thermoplastic resin composition prepared by dynamically heat-treating a thermoplastic resin using a carbon radical inducing agent and well-balanced in rigidity, impact resistance, flexibility and moldability.
Thermoplastic resins are used in various industrial fields as materials superior in moldability. The utilization field of thermoplastic resins has been expanded by blending them for modification with heterogeneous or homogeneous resins or fillers having various properties. Further, various attempts have been made for attaining effects of such blending, e.g. improvement of impact resistance and heat resistance, by heat-treating the resulting mixtures dynamically. As an example, there is known a process of heat-treating a thermoplastic resin dynamically using an organic peroxide.
However, the composition obtained by such process using an organic peroxide is desired to be remedied in the following points although it has advantages. For example, as shown in U.S. Pat. No. 3,806,558, a free radical forming agent typified by organic peroxides is used, so in the case where the thermoplastic resin used is an organic peroxide non-crosslinked type resin such as, for example, a polypropylene resin, although the resulting composition will exhibit good fluidity during injection molding, the organic peroxide remaining in the composition will deteriorate the thermal stability and weathering resistance and there will occur a thermal decomposition of the organic peroxide rapidly, resulting in that a molecular cutting reaction is unavoidable, thus leading deterioration of mechanical characteristics such as yield tensile strength, bending strength and flexural modulus.
Besides, if the said composition is used in extrusion or blow molding, there will arise such problems as deteriorated anti-drawdown property, surface roughening of parison and deficient elongation. It has also been pointed out that when the composition is used in injection molding, the gloss of the resulting molded product is deteriorated, thus affecting the beauty of the product as commodity.
On the other hand, in the case where the thermoplastic resin used is an organic peroxide crosslinked type resin such as a polyethylene resin, it becomes difficult to perform molding because the fluidity of the resulting composition is deteriorated markedly, so it is required that the amount of an organic peroxide used be extremely small. In this case, it is difficult to handle such trace amount of an organic peroxide. Further, in the use of an organic peroxide there inevitably arise problems in point of stability and safety during storage and dynamic heat treatment of a free radical forming agent, as well as thermal decomposition loss caused by the deposition on the inner wall of a processing machine. Therefore, it has been desired to solve these problems.
The following processes are known as processes for crosslinking a thermoplastic resin containing rubber and having a carbon-carbon unsaturated bond.
As the first process, the use of a sulfur-based crosslinking agent is proposed in U.S. Pat. No. 4,130,535. However, when such thermoplastic resin is dynamically heat-treated in the presence of a sulfur-based crosslinking agent, which causes the formation of sulfur radical, not only a very offensive odor is emitted at an ordinary kneading temperature, but also the resulting composition emits an offensive odor. This offensive odor of the composition is emitted again in a plasticizing step during molding, thus deteriorating the commercial value markedly. Moreover, since this composition is colored in deep yellowish red, the coloring freedom of the composition is restricted. Further, during use over a long period, there may occur discoloration due to bleeding of the sulfur compound and hence the application field is restricted.
As the second process, it is proposed in U.S. Pat. No. 4,311,628 and Japanese Patent Publication No. 19421/1979 to use a crosslinking agent comprising a halogenated phenolic resin or a phenol-formaldehyde resin with a halide incorporated therein. However, since the active halogen is liberated during crosslinking reaction, the resulting composition is discolored to black and thus the coloring freedom is lost. Besides, the fluidity of the composition is not good.
As the third process, in the above Japanese Patent Publication No. 19421/1979 it is proposed to use a quinone dioxime compound for crosslinking. However, since quinone dioximes are dark purple, the coloring freedom of the resulting composition is greatly restricted, and a pungent odor is emitted during dynamic heat treatment. Also as to the composition obtained by this process, it cannot be said that the fluidity thereof during molding is good.
As the fourth process, in U.S. Pat. Nos. 4,104,210 and 4,130,535 there is shown an example of using a bismaleimide compound or a combined use thereof with a thiazole compound. In the former, N,N'-m-phenylene bismaleimide is used for a highly unsaturated diene rubber, but it must be used in a large amount for attaining a predetermined crosslinking effect, thus giving rise to problems such as coloration of the resulting composition and bleeding of unreacted portion. In the latter, N,N'-m-phenylene bismaleimide is also used in polypropylene/EPDM system, but as to the effect of modification by dynamic heat treatment, extremely unsatisfactory results have been reported. Further, since bismaleimide compounds are generally expensive, the use thereof in a large amount causes an increase of cost.
Thus, although various crosslinking processes are known, it is desired to develop a more efficient process.
Having made extensive studies in view of the above-mentioned points, the present inventors found out a crosslinking reaction using a carbon radical inducing agent not causing a reckless and excessive crosslinking reaction as a drawback of organic peroxides in the prior art. It is the object of the invention to provide a thermoplastic resin composition prepared by such crosslinking reaction of a thermoplastic resin using a carbon radical inducing agent and free of the drawbacks of the conventional processes.